1. Field of the Invention
The present invention relates to a resin molding which is difficult to mold integrally and which is obtained by separately molding a plurality of resin molded parts each having a joining portion and mating these joining portions into one another to integrally join the molded parts together, as well as a method of manufacturing this resin molding and a resin injecting apparatus used for this method.
2. Description of the Related Art
It is contemplated that a resin molding that is difficult to mold integrally may be manufactured by separately pre-molding a plurality of resin molded parts, mating joining portions molded in these molded parts into one another, and injecting an adhesive or a resin into these joining portions to integrate the parts. For example, a cassette type toner cartridge 1 such as the one shown in FIG. 1, which is used in an electrophotographic device, comprises a cartridge main body 2 and a side cover 3 disposed at a side of the cartridge main body 2. It is essentially difficult to mold this apparatus in a single injecting step. Thus, attempts are made to separately inject these parts, integrate the parts together using a joining portion 4, and fill a molten resin into the joining portion 4 to secure them.
Attempts are also made to subject such resin moldings to a recycle process to reuse them as new resin moldings if they are damaged or used. What is important in such a recycle process is that the resin molding is composed substantially of a single material. In this connection, for resin moldings designed so that their joining portions are integrally connected together using an adhesive, the adhesive is foreign to the resin constituting the resin molding. This deteriorates recyclability. Resin moldings obtained by injecting the same molten resin as or a molten resin similar to that of the resin molding into the joining portion are more preferable in terms of recyclability.
The use of a hot melting apparatus or an injection molding apparatus is expected as a method of injecting a molten resin into the joining portion between the resin molded parts.
When the hot melting apparatus is used, it is necessary to keep a tip portion of an injection gun of the hot melting apparatus in non-contact with the joining portion between the molded parts and to supply a molten resin from the tip of the injection gun to the joining portion between the molded parts.
When a common injection molding apparatus 100 such as the one shown in FIG. 6 is used, a dies set 101 is provided which is composed of a fixed die 101a and a movable die 101b and formed with a cavity corresponding to the cartridge main body 2 and the side cover 3, combined with each other. A resin injecting apparatus 103 is provided on a frame 102 of the injection molding apparatus 100. The resin injecting apparatus 103 comprises a hopper 105 that stores resin pellets 104 in a solid state, a heating cylinder 106 that heats and molds the resin pellets 104, and a screw driving device 108 that rotates and reciprocates a screw 107 arranged inside the heating cylinder 106. The screw driving device 108 advances the screw 107 to meter a molten resin 109. A die open and close driving apparatus 110 comprises a die opening and closing cylinder 111 that reciprocates a movable plate 111a in a longitudinal direction in the FIG. 6. The fixed die 101a is fixed to a fixed plate 111b. The movable die 101b is fixed to the movable plate 111a. 
In a molding operation using the injection molding apparatus 100, the movable plate 111a is moved backward, the cartridge main body 2 and the side cover 3 are set in the die 101, and then the movable plate 111a is closed to set the cartridge main body 2 and the side cover 3 in the die 101. The fixed die 101a fixed to the fixed plate 111b has a hot runner 112 heated so as not to solidify the molten resin 109, injected from the heating cylinder 106, a gate 113 following the hot runner 112, a gate pin 114 that opens and closes the gate 113, a gate pin driving cylinder 115 that drives the gate pin 114, and a cooling fluid passage 116 through which a cooling fluid is passed to cool the gate 113. Accordingly, after the gate 113 has been opened using the gate pin 114, the molten resin 109 can be injected into the joining portion 4 between the cartridge main body 2 and the side cover 3. After the molten resin 109 has completely been injected, the gate pin 114 is advanced to close the gate 113. Then, the molten resin 109 filled into the joining portion 4 is thus cooled and solidified to integrate the cartridge main body 2 with the side cover 3. Subsequently, the die opening and closing cylinder 111 is activated to move the movable plate 111a backward. The movable die 101b fixed to the movable plate 111a is thus opened to allow the integrated cartridge main body 2 and side cover 3 to be removed.
When the hot melt apparatus is used to fill the molten resin into the joining portion 4 between the cartridge main body 2 and the side cover 3 as shown in FIG. 1, a tip portion of an injection gun of the hot melt apparatus must be kept in non-contact with the joining portion 4 between the cartridge main body 2 and the side cover 3. Thus, depending on the shapes of a cavity in the joining portion 4 into which the molten resin is filled or the viscosity of the molten resin, it may be difficult to completely fill the molten resin into these cavitys or appropriately maintain the esthetics of the surface of the joining portion after the injection.
On the other hand, when the injecting molding apparatus 100 as shown in FIG. 6 is utilized to inject the molten resin 109 into the joining portion 4 between the cartridge main body 2 and the side cover 43, such inconveniences do not occur as occur if the above-described hot melt apparatus is used. However, the injection molding apparatus 100 for molding and injecting the resin pellets 104 into the joining portion 4 further incorporates the hot runner 112 that guides the molten resin 109 to the joining portion 4, and the like. The injection molding apparatus 100 also requires the dies set 101 for holding the toner cartridge 1. Thus, disadvantageously, a dedicated facility is required, thus increasing installation spaces and facility costs. Furthermore, the injection molding apparatus itself is expensive and cumbersome to handle.